In 1979, top climate scientists led by Jule Charney published a report estimating that if we double the amount of carbon dioxide in the atmosphere from pre-industrial levels of 280 ppm to 560 ppm, temperatures will warm by 3 ± 1.5°C. Four decades later, ‘climate sensitivity’ estimates remain virtually unchanged, but some climate contrarians have argued that the number is at the low end of that range, around 2°C or less.
It’s an important question because if the contrarians are right, the 2°C resulting global warming would represent significantly less severe climate change consequences than if mainstream climate scientists are right and temperatures rise by 3°C. It would also mean our remaining carbon budget for meeting the 2°C Paris target is about twice as large than if the mainstream consensus is right. If the consensus is correct, we’re on pace to blow through the remaining Paris carbon budget by around 2030.